Ultrawideband, Low-Profile, and Low-RCS Conformal Phased Array With Capacitance-Integrated Balun and Multifunctional Meta-Surface

In this article, a 2–18 GHz phased array antenna with low-profile, low radar cross section, (RCS) and cylindrically conformal shape is presented. To achieve 9:1 impedance bandwidth with extra-low profile, the distributed capacitance structure is added into the feeding balun instead of the traditional shorting strips for the resonance suppression. This structure can avoid introducing the parasitic loop-mode, the elimination of which generally increases the antenna profile based on existing methods. Furthermore, to improve the impedance matching without prominently increasing the antenna profile, a triply-layer folded meta-surface (MS) is designed and enables the wide-scanning capacity for the proposed antenna. In addition, by etching the orthogonally polarized slots on the folded MS, the 0°/180° reflection phase for the orthogonal-polarized incident wave can be achieved. The etched slots are tightly and periodically located to improve the bandwidth of 0°/180° reflection phase and maintain the impedance matching. When an incident wave with the orthogonal polarization arrives at the array, an ultrawideband RCS reduction can be achieved and the radiating performance is maintained, owning to the multifunctional MS without lossy loads. A $19\times19$ prototype array is fabricated and measured to validate the correctness of this design. Finally, the proposed array antenna achieves the working band of 2–18 GHz and low profile together with the wide-scanning and low-RCS performance.